Detectives investigating the notorious serial killer Charles Manson are urgently attempting to use a search warrant to obtain taped conversations between one of his followers and his lawyer.

The Los Angeles Police Department's cold case unit believes the recordings could hold the key to solving more than a dozen unsolved murder cases, which resemble Manson's previous convictions.

However the tapes of Charles "Tex" Watson and his late lawyer, Bill Boyd, are among possessions caught up in a separate bankruptcy case in Texas.

The presiding judge there, Richard A Schell, has blocked the police from executing the search warrant, arguing they tried to circumvent an order he issued keeping the tapes off limits while he considers the bankruptcy case.

"This court understands and respects the desire of the LAPD to seek access to the 42-year-old tapes," Judge Schell wrote in an October 5 ruling.

"However, the LAPD has provided no explanation as to why this court should shortcut the usual procedure for determining a bankruptcy appeal given that the investigation the LAPD wishes to reopen involves murders that occurred 42 years ago."

A police spokesman Andrew Smith responded: "We're just hoping we can get these [tapes] as quickly as possible so we can get to the bottom of these cases."

Manson and his disciples were tried and convicted of eight murders, including the 1969 killing of pregnant actress Sharon Tate, the wife of film director Roman Polanski.

His apocalyptic cult committed a series of murders in upscale, mostly white neighbourhoods of Los Angeles in the hope of sparking a race war.

Manson, who was originally facing the death penalty before a change in the law in California, remains in prison for life.